The major objective of this proposal is to define requirement of zinc in man. Zinc is essential and deficiency of zinc is known to occur in man. Deficiency of zinc will be produced in human volunteers by means of a synthetic diet which will supply all the necessary dietary constituents except zinc. Zinc will be assayed in plasma, red cells, white cells, hair, beard, and nails frequently. In addition, uptake of 65Zn by red cells in vitro will be measured at suitable intervals throughout the study period. Metabolic balance studies to include zinc, copper, iron and nitrogen and fat will be performed every 4 weeks. Zinc-dependent enzymes and other biochemical parameters known to require zinc such as RNA/DNA and thymidine kinase in leucocytes, BUN, blood ammonia and ornithine transcarbamylase in plasma will be determined frequently during the study in order to define zinc sensitive parameters. This study will provide criteria for making a diagnosis of zinc-deficient state in man and a suitable dietary program requirement for zinc in man can be established. At present such knowledge is not available.